#include <bits/stdc++.h>
using namespace std;
using ll = long long;
constexpr int nax = 10005;
constexpr int INF = 1e9 + 5;
int dp[nax][nax][2];
int sz[nax];
vector<pair<int, int>> adj[nax];
void self_min(int& me, int other) {
me = min(me, other);
}
void dfs(int v, int p) {
dp[v][1][0] = dp[v][1][1] = 0;
sz[v] = 1;
for(auto& child : adj[v]) {
int u = child.first, w = child.second;
if (u == p) continue;
dfs(u, v);
for(int i = sz[v]; i >= 0; i--) {
for(int j = sz[u]; j >= 0; j--) {
self_min(dp[v][i+j][0], dp[v][i][0]+dp[u][j][0]+2*w);
self_min(dp[v][i+j][1], dp[v][i][1]+dp[u][j][0]+2*w);
self_min(dp[v][i+j][1], dp[v][i][0]+dp[u][j][1]+w);
}
}
sz[v] += sz[u];
}
// cout << v << " " << sz[v] << ": \n";
// for(int i = 0; i <= sz[v]; i++) {
// cout << i << ": " << dp[v][i][0] << " " << dp[v][i][1] << "\n";
// }
// cout << "--\n";
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, k, x;
cin >> n >> k >> x;
for(int i = 0; i < n-1; i++) {
int a, b, w;
cin >> a >> b >> w;
adj[a].push_back({b, w});
adj[b].push_back({a, w});
}
for(int i = 0; i <= n; i++) {
for(int j = 1; j <= n; j++) {
for(int p = 0; p < 2; p++) {
dp[i][j][p] = INF;
}
}
}
dfs(x, -1);
cout << dp[x][k][1] << "\n";
return 0;
}
/*
11 8 3
1 3 3
3 2 5
6 4 5
1 11 3
9 1 2
9 10 2
3 7 10
6 7 1
7 8 1
7 5 1
*/
